This invention relates to an apparatus for controlling a throttle valve position to retain the speed of running of an automotive vehicle within a range having a predetermined width.
Automotive vehicle speed control apparatus have been employed in some types of automotive vehicle for providing automatic control of the vehicle speed at a target value by adjusting the engine carburetor throttle valve in a direction which eliminates any deviation of the acutal vehicle speed value from the target value. Under such vehicle speed control, it is not necessary for the driver to continually depress the accelerator pedal when the automotive vehicle is intended to run at a constant speed on an express highway. One example of such automotive vehicle speed control apparatus is disclosed in Japanese Patent Kokai No. 59-58134.
In the conventional vehicle speed control apparatus, the throttle valve position is changed in an amount proportional to the deviation of the acutal vehicle speed value from the target value if the deviation moves out of an insensible range within which the passenger is insensible to any vehicle speed change. The required throttle valve position change should also be proportional to the target value since the response to changes in vehicle speed is slower to a change in throttle valve position at a higher vehicle speed. In addition, the response time of the change in vehicle speed to a throttle valve position change tends to vary with variations in engine performance, aerodynamic efficiency, throttle valve position, and other characteristics. In order to provide good vehicle constant-speed control, therefore, it is required to overcome this tendency by calculating the insensible range and the required throttle-valve position change using different proportional constants for different automotive vehicles.
In addition, the conventional vehicle speed control apparatus tend to create a hunting problem which results in repeated vehicle speed changes at short intervals for automotive vehicles having such a characteristic that the vehicle speed changes in slow response to a change in the position of the throttle valve and a surge problem which results in vehicle acceleration changes repeated at short intervals for automotive vehicles having such a characteristic that the vehicle speed changes in extremely fast response to a change in the position of the throttle valve.